Propeller phase synchronizer controls, or SYNCHRONPHASER.RTM.(SYNCHRONPHASER is a registerd trademark of United Technologies Corporation) are known in the prior art for use on multi-engine, propeller driven aircraft to maintain a selected phase angle relationship between a selected "master" propeller and each of the other propellers (designed "slave"propellers). When the propellers are synchronized the aircraft fuselage experiences minimum acoustic noise and vibration.
The prior art synchronizer controls utilize an electrical pulse to detect the time (T) that each propeller is at a particular blade orientation. This time relationship between successive pulses of the master propeller blakes (T.sub.M) and the blade pulses of the slave propeller(s) (T.sub.D) is shown in FIG. 1.
The phase relation between any two propellers is then determined from a combination (a) measurement of the time interval between successive pulses from a master propeller (T.sub.M) and (b) a measurement of the time delay of a pulse from the master propeller to the next succeeding pulse from a slave (or other) propeller (T.sub.D). An example of the time relationship of the pulses (T) from two propellers (designated master propeller (T.sub.M) and slave propeller (T.sub.D) ) and the method for determining the propeller phase relationship (.phi..sub.s) is shown in equation 1. ##EQU1##
Where NP is the number of pulses per revolution of the propeller.
In equation 1, an increasing delay in the interval (T.sub.D) yields an increasing sensed phase (.phi..sub.s) until the slave pulse is sufficiently delayed to occur with the next master pulse. As the pulses T.sub.D and T.sub.M align, the value of T.sub.D abruptly changes from the value of t.sub.m to 0, resulting in the sensed phase abruptly changing from a maximum value to 0. The sensed phase (.phi..sub.s) in comparison to the actual phase is shown in FIG. 2.
Phase error (.phi..sub.E) is sensed phase .phi..sub.s minus a reference phase (.phi..sub.REF) as shown in equation 2. EQU .phi..sub.E =.phi..sub.S -.phi..sub.REF ti 2
The (.phi..sub.REF) in equation 2 is the phase offset from perfect alignment of blades which is often necessary in providing the lowest noise synchronization of propellers. If minimum noise and vibration occur when the pulses from the master and slave propellers are coincident then no (.phi..sub.REF) is required. .phi..sub.REF is determined by the characteristics of the particular aircraft and its engines.
The present prior art phase synchronizer controls typically utilize one electrical pulse per propeller revolution (NP=1) so that sensed phase between discontinuities provide a phase error measurement up to .+-.180.degree. . In addition, present phase controls utilize some form of "start circuit" to assure that the master and slave propeller speeds are nearly the same so that the phaser control laws can prevent the phase error from reaching the sign ambiguity that occurs at the phase measurement discontinuity.